1. Field of the Invention
The present invention pertains to photoimaging and, in particular, the use of photoresists (positive-working and/or negative-working) for imaging in the production of semiconductor devices. The present invention also pertains to photoresists containing polymer compositions having high UV transparency (particularly at short wavelengths, e.g., 157 nm or 193 nm) which are useful as base resins in resists and potentially in many other applications.
2. Background
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems such as those described in Introduction to Microlithography, Second Edition by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. A latent image is thereby produced which can be processed into a useful image for semiconductor device fabrication.
Although the polymer product itself may be photoactive, generally a photosensitive composition contains one or more photoactive components in addition to the polymer product. Upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the rheological state, solubility, surface characteristics, refractive index, color, electromagnetic characteristics and/or other such physical or chemical characteristics of the photosensitive composition as described in the Thompson et al. publication supra.
For imaging very fine features at the submicron level in semiconductor devices, electromagnetic radiation in the far or extreme ultraviolet (UV) is needed. Positive working photoresists generally are utilized for semiconductor manufacture. Lithography in the UV at 365 nm (I-line) using novolak polymers and diazonaphthoquinones as dissolution inhibitors is a currently established chip technology having a resolution limit of about 0.35-0.30 micron. Lithography in the far UV at 248 nm using p-hydroxystyrene polymers is known and has a resolution limit of 0.35-0.18 nm. There is strong impetus for future photolithography at even shorter wavelengths, due to a decreasing lower resolution limit with decreasing wavelength (i.e., a resolution limit of 0.18-0.12 micron for 193 nm imaging and a resolution limit of about 0.07 microns for 157 nm imaging). Photolithography using 193 nm exposure wavelength (obtained from an argon fluorine (ArF) excimer laser) is a leading candidate for future microelectronics fabrication using 0.18 and 0.13 xcexcm design rules. Photolithography using 157 nm exposure wavelength (obtained from a fluorine excimer laser) is a leading candidate for future microlithography further out on the time horizon (beyond 193 nm). There is a strong need for photoresist materials having sufficient transparency and other required properties at these very short wavelengths. The opacity of traditional near UV and far UV organic photoresists at 193 nm or shorter wavelengths precludes their use in single-layer schemes at these short wavelengths.
Photoresist compositions, also referred to herein as xe2x80x9cresistsxe2x80x9d, suitable for imaging at 157 nm are presently unknown. The main reason for this current status of 157 nm resists is that all conventional resist materials absorb to a significant degree at this wavelength to preclude their use as component(s) in 157 nm resists.
There is a critical need for suitable novel resist compositions for use at 193 nm, and particularly at 157 nm, or lower wavelengths, that have not only high transparency at these short wavelengths but also suitable other key properties, including good plasma etch resistance, development characteristics, and adhesive properties.
In some embodiments, the invention is a photoresist comprising:
(a) a polymer comprising:
(i) a repeat unit derived from at least one ethylenically unsaturated compound containing a fluoroalcohol functional group having the structure:
xe2x80x94C(Rf)(Rfxe2x80x2)OH
xe2x80x83wherein Rf and Rfxe2x80x2 are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or taken together are (CF2)n wherein n is 2 to about 10; and
(ii) a repeat unit derived from at least one ethylenically unsaturated compound having the structure:
(H)(R1)Cxe2x95x90C(R2)(CN)
xe2x80x83wherein R1 is a hydrogen atom or CN group; R2 is C1-C8 alkyl group, hydrogen atom, or CO2R3 group, where R3 is C1-C8 alkyl group or hydrogen atom; and
(b) at least one photoactive component.
In other embodiments, the invention is a process for preparing a photoresist image on a substrate comprising, in order:
(A) applying a photoresist composition on a substrate to form a photoresist layer, wherein the photoresist composition comprises:
(i) a polymer comprising:
(a) a repeat unit derived from at least one ethylenically unsaturated compound containing a fluoroalcohol functional group having the structure:
xe2x80x94C(Rf)(Rfxe2x80x2)OH
xe2x80x83wherein Rf and Rfxe2x80x2 are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or taken together are (CF2)n wherein n is an integer ranging from 2 to about 10; and
(b) a repeat unit derived from at least one ethylenically unsaturated compound having the structure:
(H)(R1)Cxe2x95x90C(R2)(CN)
xe2x80x83wherein R1 is hydrogen atom or CN group; R2 is an alkyl group of 1 to about 8 carbon atoms, hydrogen atom, or CO2R3 group, wherein R3 is an alkyl group of 1 to about 8 carbon atoms or hydrogen atom; and;
(ii) at least one photoactive component;
(B) imagewise exposing the photoresist layer to form imaged and non-imaged areas; and
(C) developing the exposed photoresist layer having imaged and non-imaged areas to form the photoresist image on the substrate.
Typically the photoresist composition is further comprised of a solvent, and the process (as given supra) further comprises, between steps (A) and (B), a step of drying the photoresist composition to substantially remove solvent and thereby form a photoresist layer on the substrate.
With respect to some specific embodiments of the photoresists and associated processes of this invention, the polymer (nitrile/fluoroalcohol-containing polymer) present as a component in the photoresists preferably has an absorption coefficient of less than 5.0 xcexcmxe2x88x921 at a wavelength of 157 nm. In other certain embodiments, the (nitrile/fluoroalcohol-containing) polymer is further comprised of protected acid groups and/or aliphatic polycyclic functionality. In some embodiment(s), the photoactive component of the photoresists and associated processes is a photoacid generator. In still other certain embodiment(s), the photoresists and associated processes are further comprised of a dissolution inhibitor.
A key characteristic of the polymers (and photoresists comprised of the polymers) of this invention is the cooperative combination in the polymers of repeat unit(s) containing a fluoroalcohol functional group with repeat units containing the cyano (CN) group. Another characteristic of the polymer is that it lacks amounts of functionality sufficient to cause the polymer to detrimentally absorb in the extreme and far UV. The presence of repeat units containing fluoroalcohol functional groups is desirable in order for the polymers to be sufficiently acidic to be developable in basic aqueous media while at the same time minimizing the need for having alternate functionality, such as carboxylic acid, present for developability, which may lead to too high absorptions in the deep UV for these materials to be used in resists at these low imaging wavelengths (e.g., 157 nm or 193 nm). The presence of repeat units containing cyano (CN) functionality in these polymers is desirable in order for the polymers to possess high optical transparency, i.e., to have low optical absorptions in the extreme and far UV, and improved etch resistance, while at the same time providing polar functionality that significantly imparts increased developability to these polymers and affords suitable development characteristics with lower levels of fluoroalcohol functional groups than would otherwise, usually, be required. The minimization of functionality, such as aromatic groups, which absorb in the extreme ultraviolet in the repeat units of the polymers is desirable in order for these polymers to possess high optical transparency.
A given nitrile/fluoroalcohol-containing polymer comprising a repeat unit derived from at least one ethylenically unsaturated compound containing a fluoroalcohol functional group according to this invention has fluoroalkyl groups present as part of the fluoroalcohol functional group.
These fluoroalkyl groups are designated as Rf and Rfxe2x80x2, which can be partially fluorinated alkyl groups or fully fluorinated alkyl groups (i.e., perfluoroalkyl groups). The groups designated by Rf and Rfxe2x80x2 are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or, taken together, are (CF2)n wherein n is 2 to about 10. The terms xe2x80x9ctaken togetherxe2x80x9d mean that Rf and Rfxe2x80x2 are not separate, discrete fluorinated alkyl groups, instead together they form a ring structure such as is illustrated below in the case of a 5-membered ring: 
Rf and Rfxe2x80x2 can be partially fluorinated alkyl groups without limit according to the invention except that there must be a sufficient degree of fluorination present to impart acidity to the hydroxyl (xe2x80x94OH) of the fluoroalcohol functional group, such that the hydroxyl proton is substantially removed in basic media, such as in aqueous sodium hydroxide solution or tetraalkylammonium hydroxide solution. According to the invention, there will usually be sufficient fluorine substitution present in the fluorinated alkyl groups of the fluoroalcohol functional group such that the hydroxyl group will have a pKa value of less than or equal to about 11. In preferred cases according to the invention, there will be sufficient fluorine substitution present in the fluorinated alkyl groups of the fluoroalcohol functional group such that the hydroxyl group will have a pKa value between about 4 and about 11. More preferably, Rf and Rfxe2x80x2 are independently perfluoroalkyl group of 1 to 5 carbon atoms, and, most preferably, Rf and Rfxe2x80x2 are both trifluoromethyl (CF3) groups.
Some illustrative, but nonlimiting, examples of monomers falling within the generalized structural formula (given supra) containing a fluoroalcohol functional group and within the scope of the invention are presented below: 
For a particular embodiment of the invention, the fluoroalcohol functional group has the structure:
xe2x80x94XCH2C(Rf)(Rfxe2x80x2)OH
wherein Rf and Rfxe2x80x2 are the same or different fluoroalkyl groups of from 1 to about 10 carbon atoms or taken together are (CF2)n wherein n is 2 to about 10; X is selected from the group consisting of oxygen atom, sulfur atom, nitrogen atom, phosphorous atom, other Group VB element, and other Group VIB element (Sargent Welch Periodic Table, 1979, Sargent Welch Scientific Company, Skokie, Ill.). The terms xe2x80x9cother Group VA elementxe2x80x9d and xe2x80x9cother Group VIA elementxe2x80x9d are understood to mean any other element in one of these groups of the periodic table that is other than the recited elements (i.e., oxygen, sulfur, nitrogen, phosphorous) in these groups. Oxygen is the preferred group.
At least a portion of the nitrile functionality that is present in the nitrile/fluoroalcohol polymers of this invention results from incorporation of repeat unit(s) derived from at least one ethylenically unsaturated compound having at least one nitrile group and having the structure:
(H)(R1)Cxe2x95x90C(R2)(CN)
wherein R1 is H or CN; R2 is C1-C8 alkyl, H, or CO2R3 where R3 is C1-C8 alkyl group or H. CN represents a cyano (nitrile) group. Acrylonitrile, methacrylonitrile, fumaronitrile (trans-1,2-dicyanoethylene), and maleonitrile (cis-1,2-dicyanoethylene) are preferred. Acrylonitrile is most preferred.
The nitrile/fluoroalcohol polymers preferably are characterized in having a repeat unit derived from at least one ethylenically unsaturated compound containing the fluoroalcohol functional group that is present in the nitrile/fluoroalcohol polymers from about 10 to about 60 mole percent and a repeat unit derived from the at least one ethylenically unsaturated compound containing at least one nitrile group present in the polymer from about 20 to about 80 mole percent. The nitrile/fluoroalcohol polymers more preferably with respect to achieving low absorption coefficient values are characterized in having a repeat unit derived from at least one ethylenically unsaturated compound containing the fluoroalcohol functional group that is present in the polymers at less than or equal to 45 mole percent, and, still more preferably, at less than or equal to 30 mole percent with relatively small amounts of a repeat unit containing the nitrile group making at least a portion of the balance of the polymer.
It is recognized though that there usually will be a minimal level of fluoroalcohol functional groups present for the polymer to be soluble and/or dispersible in aqueous basic solutions (e.g., standard 0.262 N TMAH solution) that is required for developability. This minimal level can vary with the structure of the moiety bearing the fluoroalcohol functional group and with the selection of comonomer(s) and their levels that are present in the polymers as well as with other parameters of the polymer such as molecular weight. Some specific illustrative examples of polymers having fluoroalcohol which were found to have too low solubility in aqueous basic media are AN/IBFA (76/24) and AN/IBFA/NB (61/21/18). One skilled in the art can determine readily whether a given polymer is soluble/dispersible or not in aqueous basic solutions. This requirement for having a suitable minimal level of fluoroalcohol functional group in the polymer to impart base solubility/dispersibility to the polymer is usually balanced against keeping the level as low as feasible in order to maximize transparency of the polymer in the far/extreme UV range of the electromagnetic spectrum.
In one embodiment of the invention, the photoresist includes at least one protected functional group. The functional group of the at least one protected functional group is, typically, selected from the group consisting of acidic functional groups and basic functional groups. Nonlimiting examples of functional groups of the protected functional group are carboxylic acids and fluoroalcohols. At least one fluoroalcohol group of the polymer or other functional group of the polymer (such as a carboxylic acid group) may be protected. In an alternative embodiment, an additive composition containing protected functional groups may be incorporated into the photoresist composition. If such an additive is included, none, some or all of the functional groups of the polymer may be protected. Thus, the photoresist composition may comprise at least one member selected from the group consisting of a carboxylic acid, a fluoroalcohol (from the the nitrile/fluoroalcohol polymer but it can additionally be from an additive), a protected fluoroalcohol, and a protected carboxylic acid.
A given nitrile/fluoroalcohol polymer of this invention can be further comprised of protected acidic groups. In these embodiment(s), the percentage of repeat units of the nitrile/fluoroalcohol polymer containing protected acidic groups broadly ranges from about 1 to about 70 mole percent; preferably ranges from 5 to 55 mole percent; and more preferably ranges from 10 to 45 mole percent.
In another embodiment, a nitrile/fluoroalcohol polymer of this invention can include aliphatic polycyclic functionality. In this embodiment, the percentage of repeat units of the nitrile/fluoroalcohol polymer containing aliphatic polycyclic functionality ranges from about 1 to about 70 mole percent; preferably from about 10 to about 55 mole percent; and more preferably ranges from about 20 to about 45 mole percent.
The nitrile/fluoroalcohol polymers of this invention can contain additional functional groups beyond those specifically mentioned herein with the proviso that, preferably, aromatic functionality is absent in the nitrile/fluoroalcohol polymers. The presence of aromatic functionality in these polymers has been found to detract from their transparency and result in their being too strongly absorbing in the deep and extreme UV regions to be suitable for use in photoresists that are imaged at these wavelengths.
In many embodiments according to this invention, a given nitrile/fluoroalcohol polymer preferably has an absorption coefficient of less than 5.0 xcexcmxe2x88x921 at a wavelength of 157 nm, more preferably less than 4.0 xcexcmxe2x88x921 at this wavelength, still more preferably less than 3.5 xcexcmxe2x88x921 at this wavelength, and most preferably less than 3.00 xcexcmxe2x88x921 at this wavelength.
The polymers of this invention can be synthesized by the solution polymerization procedure reported in the examples. Any of the commonly used organic solvents known to those skilled in the art can be used as the solvent for polymerization. The solvent used for the polymerization depends upon the composition of the polymers. The temperature for the polymerization can be at the reflux temperature of the polymerization reaction mixture or lower if the polymerization is carried out at atmospheric pressure and reflux conditions. If the polymerization is carried out under pressure, the polymerization temperature can be in the range of about 20 to about 150xc2x0 C. Alternatively the above polymers can be synthesized by (a) emulsion or (b) suspension (bead) polymerization procedures.
In some embodiments of this invention, the polymer is a branched polymer comprising one or more branch segment(s) chemically linked along a linear backbone segment. The branched polymer can be formed during free radical addition polymerization of at least one ethylenically unsaturated macromer component and at least one ethylenically unsaturated comonomer. The ethylenically unsaturated macromer component has a number average molecular weight (Mn) between a few hundred and about 40,000 and the linear backbone segment resulting from the polymerization has a number average molecular weight (Mn) between about 2,000 and about 500,000. The weight ratio of the linear backbone segment to the branch segment(s) is within a range of about 50/1 to about 1/10, and preferably within the range of about 80/20 to about 60/40. Preferably the macromer component has a number average molecular weight (Mn) from about 500 to about 40,000 and more preferably of about 1,000 to about 15,000. Typically such an ethylenically unsaturated macromer component can have a number average molecular weight (Mn) equivalent to there being from about 2 to about 500 monomer units used to form the macromer component, preferably between about 30 and about 200 monomer units, and most preferably about 10 to about 50 monomer units.
In a preferred embodiment, the branched polymer contains from about 25% to about 100% by weight of compatibilizing groups, i.e., functional groups present to increase compatibility with the photoacid generator, preferably from about 50% to about 100% by weight, and more preferably from about 75% to about 100% by weight. Suitable compatibilizing groups for ionic photoacid generators include, but are not limited to, both non-hydrophilic polar groups and hydrophilic polar groups. Suitable non-hydrophilic polar groups include, but are not limited to, cyano (xe2x80x94CN) and nitro (xe2x80x94NO2). Suitable hydrophilic polar groups include, but are not limited to protic groups such as hydroxy (OH), amino (NH2), ammonium, amido, imido, urethane, ureido, or mercapto; or carboxylic (CO2H), sulfonic, sulfinic, phosphoric, or phosphoric acids or salts thereof. Preferably, compatibilizing groups are present in the branch segment(s).
Preferably, the protected acidic groups, present in the branched polymer, produce fluoroalcohol groups and/or carboxylic acid groups after exposure to WV or other actinic radiation and subsequent post-exposure baking (i.e., during deprotection). The branched polymer when present in the photosensitive compositions of this invention, typically will contain between about 3% to about 40% by weight of monomer units containing protected acidic groups, preferably between about 5% to about 50%, and more preferably between about 5% to about 20%. The branch segments of such a preferred branched polymer typically contain between 35% to 100% of the protected acidic groups present. Such a branched polymer when completely unprotected (all protected acidic groups converted to free acidic groups) has an acid number between about 20 and about 500, preferably between about 30 and about 330, and more preferably between about 30 and about 130, and analogously the ethylenically unsaturated macromer component preferably has an acid number of about 20 and about 650, more preferably between about 90 and about 300 and the majority of the free acidic groups are in the branch segments.
In a specific embodiment, the branched polymer comprises one or more branch segments chemically linked along a linear backbone segment wherein the branched polymers have a number average molecular weight (Mn) of about 500 to about 40,000. The branched polymer contains at least about 0.5% by weight of branch segments. The branch segments, also known as polymer arms, typically are randomly distributed along the linear backbone segment. The xe2x80x9cpolymer armxe2x80x9d or branch segment is a polymer or oligomer of at least two repeating monomer units, which is attached to the linear backbone segment by a covalent bond. The branch segment, or polymer arm, can be incorporated into the branched polymer as a macromer component, during the addition polymerization process of a macromer and a comonomer. A xe2x80x9cmacromerxe2x80x9d for the purpose of this invention, is a polymer, copolymer or oligomer of molecular weight ranging from several hundred to about 40,000 containing a terminal ethylenically unsaturated polymerizable group. Preferably the macromer is a linear polymer or copolymer end capped with an ethylenic group. Typically, the branched polymer is a copolymer bearing one or more polymer arms, and preferably at least two polymer arms, and is characterized in that between about 0.5 and about 80 weight %, preferably between about 5 and about 50 weight % of the monomeric components used in the polymerization process is a macromer. Typically, comonomer components used along with the macromer in the polymerization process likewise contain a single ethylenic group that can polymerize with the ethylenically unsaturated macromer.
The ethylenically unsaturated macromer and the resulting branch segment of the branched polymer, and/or the backbone of the branched polymer, can have bonded thereto one or more protected acidic groups. For the purposes of this invention, a xe2x80x9cprotected acidic groupxe2x80x9d means a functional group which, when deprotected, affords free acidic functionality that enhances the solubility, swellability, or dispersibility in aqueous environments, of the macromer and/or the branched polymer to which it is bonded. The protected acidic group may be incorporated into the ethylenically unsaturated macromer and the resulting branch segment of the branched polymer, and/or the backbone of the branched polymer, either during or after their formation.
While addition polymerization using a macromer and at least one ethylenically unsaturated monomer is preferred for forming the branched polymer, all known methods of preparing branched polymers using either addition or condensation reactions can be utilized in this invention. Furthermore, use of either preformed backbones and branch segments or in situ polymerized segments are also applicable to this invention.
The branch segments attached to the linear backbone segment can be derived from terminally ethylenically unsaturated macromers prepared by methods well known in the art, such as provided in the general descriptions in U.S. Pat. No. 4,680,352 and U.S. Pat. No. 4,694,054.
The branched polymer may be prepared by any conventional addition polymerization process. The branched polymer, or comb polymer, may be prepared from one or more compatible ethylenically unsaturated macromer components and one or more compatible, conventional ethylenically unsaturated macromer components and one or more compatible, conventional ethylenically unsaturated monomer component(s). Preferred addition polymerizable, ethylenically unsaturated monomer components are acrylonitrile, methacrylonitrile, fumaronitrile, maleonitrile, protected and/or unprotected unsaturated fluoroalcohols, and protected and/or unprotected unsaturated carboxylic acids.
The compositions of this invention contain at least one photoactive component (PAC) that usually is a compound that affords either acid or base upon exposure to actinic radiation. If an acid is produced upon exposure to actinic radiation, the PAC is termed a photoacid generator (PAG). If a base is produced upon exposure to actinic radiation, the PAC is termed a photobase generator (PBG).
Suitable photoacid generators for this invention include, but are not limited to, 1) sulfonium salts (structure I), 2) iodonium salts (structure II), and 3) hydroxamic acid esters, such as structure III. 
In structures I-II, R4-R6 are independently substituted or unsubstituted aryl or substituted or unsubstituted C1-C20 alkylaryl (aralkyl). Representative aryl groups include, but are not limited to, phenyl and naphthyl. Suitable substituents include, but are not limited to, hydroxyl (xe2x80x94OH) and C1-C20 alkyloxy (e.g., ClOH21O). The anion Xxe2x80x94 in structures Ixe2x80x94II can be, but is not limited to, SbF6-(hexafluoroantimonate), CF3SO3-(trifluoromethylsulfonate=triflate), and C4F9SO3-(perfluorobutylsulfonate).
The nitrile/fluoroalcohol-containing polymers of the resist compositions of this invention may contain one or more components having protected acidic fluorinated alcohol groups and/or other acidic or basic groups that can yield, by catalysis of acids or bases generated photolytically from photoactive compounds (PACs), hydrophilic acidic or basic groups which enable development of resist coatings. A given protected acidic or basic group is one that is normally chosen on the basis of its being acid or base labile, such that when photoacid or photobase is produced upon imagewise exposure, the acid or base will catalyze deprotection and production of hydrophilic acidic or basic groups that are necessary for development under aqueous conditions. In addition, the nitrile/fluoroalcohol-containing polymers may also contain acidic or basic functionality that is not protected. The nitrile/fluoroalcohol-containing polymers may contain at least one, more than one, or all fluoroalcohol groups that is/are protected. Photoresists comprised of the nitrile/fluoroalcohol-containing polymers of this invention can be heated to promote deprotection necessary for image formation. A functional group when deprotected affords free acidic functionality that enhances the solubility, swellability, and/or dispersibility in aqueous environments of the polymer to which the functional group is bonded.
Nonlimiting examples of components having protected acidic groups that yield an acidic group as the hydrophilic group upon exposure to photogenerated acid include a) esters capable of forming, or rearranging to, a tertiary cation, b) esters of lactone, c) acetal esters, d) xcex2-cyclic ketone esters, e) xcex1-cyclic ether esters, f) MEEMA (methoxy ethoxy ethyl methacrylate) and other esters which are easily hydrolyzable because of anchimeric assistance, g) carbonates formed from a fluorinated alcohol and a tertiary aliphatic alcohol. Some specific examples in category a) are t-butyl ester, 2-methyl-2-adamantyl ester, and isobomyl ester. Some specific examples in category b) are xcex3-butyrolactone-3-yl, xcex3-butyrolactone-2-yl, mavalonic lactone, 3-methyl-xcex3-butyrolactone-3-yl, 3-tetrahydrofuranyl, and 3-oxocyclohexyl. Some specific examples in category c) are 2-tetrahydropyranyl, 2-tetrahydrofuranyl, and 2,3-propylenecarbonate-1-yl.
Additional examples in category c) include various esters from addition of vinyl ethers, such as, for example, ethoxy ethyl vinyl ether, methoxy ethoxy ethyl vinyl ether, and acetoxy ethoxy ethyl vinyl ether.
Examples of components having protected acidic groups that yield a fluorinated alcohol as the hydrophilic group upon exposure to photogenerated acid or base include, but are not limited to, t-butoxycarbonyl (t-BOC), t-butyl ether, and 3-cyclohexenyl ether. Each of these protected acidic groups can be utilized in combination with the fluoroalcohol functional group of this invention to afford a protected acidic fluoroalcohol functional group. The fluoroalcohol functional group (protected or unprotected) of this invention can be used alone or it can be used in combination with one or more other acid groups, such as carboxylic acid functional group (unprotected) and t-butyl ester of carboxylic acid functional group (protected).
In this invention, often, but not always, the components having protected groups are repeat units having protected acid groups that have been incorporated in the base copolymer resins of the compositions (as discussed supra). Frequently the protected acid groups are present in one or more monomer(s) that are polymerized to form a given polymeric base resin of this invention. Alternatively, in this invention, a polymeric base resin can be formed by polymerization with an acid-containing monomer and then subsequently acid functionality in the resulting acid-containing polymer can be partially or wholly converted by appropriate means to derivatives having protected acid groups. As one specific example, a polymer of AN/IBFA/tBA (polymer containing acrylonitrile, 1,1,1-trifluoro-4-methyl-2-(trifluoromethyl)-4-penten-2-ol, and t-butyl acrylate) is a polymeric base resin within the scope of the invention having t-butyl ester groups as protected-acid groups.
Various dissolution inhibitors can be utilized in this invention. Ideally, dissolution inhibitors (DIs) for far and extreme UV resists (e.g., 193 nm resists) should be designed/chosen to satisfy multiple needs including dissolution inhibition, plasma etch resistance, and adhesion behavior of resist compositions comprising a given DI additive. Some dissolution inhibiting compounds also serve as plasticizers in resist compositions.
A variety of bile-salt esters (i.e., cholate esters) are particularly useful as DIs in the compositions of this invention. Bile-salt esters are known to be effective dissolution inhibitors for deep UV resists, beginning with work by Reichmanis et al. in 1983. (E. Reichmanis et al., xe2x80x9cThe Effect of Substituents on the Photosensitivity of 2-Nitrobenzyl Ester Deep UV Resistsxe2x80x9d, J. Electrochem. Soc. 1983, 130, 1433-1437.) Bile-salt esters are particularly attractive choices as DIs for several reasons, including their availability from natural sources, their possessing a high alicyclic carbon content, and particularly for their being transparent in the deep and vacuum UV region, (which essentially is also the far and extreme UV region), of the electromagnetic spectrum (e.g., typically they are highly transparent at 193 nm). Furthermore, the bile-salt esters are also attractive DI choices since they may be designed to have widely ranging hydrophobic to hydrophilic compatibilities depending upon hydroxyl substitution and functionalization.
Representative bile-acids and bile-acid derivatives that are suitable as additives and/or dissolution inhibitors for this invention include, but are not limited to, those illustrated below, which are as follows: cholic acid (IV), deoxycholic acid (V), lithocholic acid (VI), t-butyl deoxycholate (VII), t-butyl lithocholate (VIII), and t-butyl-3-xcex1-acetyl lithocholate (IX). Bile-acid esters, including compounds VII-IX, are preferred dissolution inhibitors in this invention. 
Some embodiments of this invention are negative-working photoresists. These negative-working photoresists comprise at least one binder polymer comprised of acid-labile groups and at least one photoactive component that affords photogenerated acid. Imagewise exposure of the resist affords photogenerated acid which converts the acid-labile groups to polar functionality (e.g., conversion of ester functionality (less polar) to acidic functionality (more polar)). Development is then done in an organic solvent or critical fluid (having moderate to low polarity), which results in a negative-working system in which exposed areas remain and unexposed areas are removed.
A variety of different crosslinking agents can be employed as required or optional photoactive component(s) in the negative-working compositions of this invention. (A crosslinking agent is required in embodiments that involve insolubilization in developer solution as a result of crosslinking, but is optional in preferred embodiments that involve insolubilization in developer solution as a result of polar groups being formed in exposed areas that are insoluble in organic solvents and critical fluids having moderate/low polarity).
The compositions of this invention can contain optional additional components. Examples of additional components which can be added include, but are not limited to, resolution enhancers, adhesion promoters, residue reducers, coating aids, surfactants, plasticizers, and Tg (glass transition temperature) modifiers.
Imagewise Exposure
The photoresist compositions of this invention are sensitive in the ultraviolet region of the electromagnetic spectrum and especially to those wavelengths xe2x89xa6365 nm. Imagewise exposure of the resist compositions of this invention can be done at many different UV wavelengths including, but not limited to, 365 nm, 248 nm, 193 nm, 157 nm, and lower wavelengths. Imagewise exposure is preferably done with ultraviolet light of 248 nm, 193 nm, 157 nm, or lower wavelengths, more preferably it is done with ultraviolet light of 193 nm, 157 nm, or lower wavelengths, and most preferably, it is done with ultraviolet light of 157 nm or lower wavelengths. Imagewise exposure can either be done digitally with a laser or equivalent device or non-digitally with use of a photomask. Suitable laser devices for digital imaging of the compositions of this invention include, but are not limited to, an argon-fluorine excimer laser with UV output at 193 nm, a krypton-fluorine excimer laser with UV output at 248 nm, and a fluorine (F2) laser with output at 157 nm. Since, as discussed supra, use of UV light of lower wavelength for imagewise exposure corresponds to higher resolution (lower resolution limit), the use of a lower wavelength (e.g., 193 nm or 157 nm or lower) is generally preferred over use of a higher wavelength (e.g., 248 nm or higher).
Development
The nitrile/fluoroalcohol-containing polymers in the resist compositions of this invention must contain sufficient functionality for development following imagewise exposure to UV light. Preferably, the functionality is acidic or protected acidic such that aqueous development is possible using a basic developer such as sodium hydroxide solution, potassium hydroxide solution, or tetramethylammonium hydroxide solution. In this invention, a given acidic-containing binder polymer for aqueous processability (aqueous development) in use is a fluoroalcohol-containing copolymer (after exposure) containing at least one fluoroalcohol functional group. The level of fluoroalcohol groups is determined for a given composition by optimizing the amount needed for good development in aqueous alkaline developer.
When an aqueous processable photoresist is coated or otherwise applied to a substrate and imagewise exposed to UV light, the polymer of the photoresist must have sufficient protected and/or unprotected acidic groups so that when exposed to UV the exposed photoresist will become developable in basic solution. In case of a positive-working photoresist layer, the photoresist layer will be removed during development in portions which are exposed to UV radiation but will be substantially unaffected in unexposed portions during development by aqueous alkaline liquids such as wholly aqueous solutions containing 0.262 N tetramethylammonium hydroxide (with development at 25xc2x0 C. usually for less than or equal to 120 seconds) or 1% sodium carbonate by weight (with development at a temperature of 30xc2x0 C. usually for less than 2 or equal to 2 minutes). In case of a negative-working photoresist layer, the photoresist layer will be removed during development in portions which are unexposed to UV radiation but will be substantially unaffected in exposed portions during development using either a critical fluid or an organic solvent.
A critical fluid, as used herein, is one or more substances heated to a temperature near or above its critical temperature and compressed to a pressure near or above its critical pressure. Critical fluids in this invention are at least at a temperature that is higher than 15xc2x0 C. below the critical temperature of the fluid and are at least at a pressure higher than 5 atmospheres below the critical pressure of the fluid. Carbon dioxide may be used for the critical fluid in the present invention. Various organic solvents can also be used as developer in this invention. These include, but are not limited to, halogenated solvents and nonhalogenated solvents. Halogenated solvents are preferred and fluorinated solvents more preferred.